This invention relates to a rotary damper for utilizing a rotational motion to effect a damping action, and relates to an improvement in the rotary damper suitable for use, for example, with a suspension of an automobile or a suspension for a rear wheel of a motor-cycle or other various apparatuses.
Conventionally, the rotary damper of this kind has been already proposed, for example, in Japanese Patent Application Laid-Open No. 12152/1989 laid open to public on Jan. 17, 1989.
That is, in the rotary damper proposed above, two sets of operating oil chambers are defined between a separate block provided on the inner wall of a casing and a vane provided on the outer periphery of a rotor, and the two sets of operating oil chambers are alternately contracted and expanded with a relative rotational motion between the casing and the rotor.
The above-described two sets of operating chambers are communicated with each other through a series of interconnecting flowpassages comprising a radial oil port bored in the rotor and an oil chamber provided in the center portion, and a damping force generating mechanism is disposed in the oil chamber of the interconnecting flowpassage to impart a flow resistance to operating oil from the operating oil chamber on the contracted side toward the operating oil chamber on the expanded side, thereby generating a predetermined damping force corresponding to the operating direction of the rotary damper by the damping force generating mechanism.
Further, on the rotor side is disposed a temperature compensating mechanism comprising an accumulator aligned in an axial direction of the above oil chamber of the interconnecting flowpassage, an oil storage chamber of the temperature compensating mechanism is communicated with the operating oil chamber through a throttle whereby overs and shorts of operating oil volume resulting from the change of temperature is compensated for by the temperature compensating mechanism and the flow rate of operating oil flowing into the oil storage chamber of the temperature compensating mechanism when the rotary damper is operated is limited by the flow resistance by the throttle.
As described above, in the above-described rotary damper, the flowing of a part of the operating oil moving from the operating oil chamber on the contracting side toward the operating oil chamber on the expanding side into the oil storage chamber of the temperature compensating mechanism is limited as less as possible by the throttle when in operation, to secure the quantity of operating oil supplied to the operating oil chamber on the expanding side to impede generation of vacuum and subsequently prevent disturbance of initial damping characteristic at the time of inversion of the rotary damper.
However, even so, when the operating oil leaks through around the separate block on the casing side and the vane on the rotary side, the damping characteristic as the rotary damper is lowered and disturbed by the leakage of the operating oil.
Of course, a greater part of the leakage of the operating oil can be prevented by applying seal members to the peripheries of the separate block and the vane. However, the seal member applied to the vane cannot seal between the basic portion of the vane and the bearing end of the casing side for supporting the rotor.
For this reason, there occurs a flow of operating oil which immediately leaks from the operating oil chamber on the contracted side to the operating oil chamber on the expanded side through a clearance between the bearing and the basis portion of the rotor without passing through the damping force generating mechanism.
Further, the lower the viscosity resulting from the rise in temperature of the operating oil is, the higher the leakage amount of the operating oil from the aforesaid portion becomes to reduce the amount of operating oil flowing through the interconnecting flowpassage and lower the damping characteristic at the damping force generating mechanism, posing an inconvenience that the temperature characteristic as the rotary damper is deteriorated.